Construction is the process of forming buildings and structures. Cranes are used in construction to move and transport materials from one place to another. One type of crane is the tower crane. Tower cranes provide a good combination of height and lifting capacity needed in the construction of tall buildings. Tower cranes are used for lifting heavy building materials like concrete slabs, steel structures, bulk sand bags; machinery equipment like power generators, cement mixing machines; and other objects.
Tower cranes generally consist of the same basic parts: the base, the tower or mast, and the slewing unit. The base is typically bolted to a large concrete pad that supports the crane. The mast connects to the base and gives the crane its height. The slewing unit is attached to the top of the mast, and includes the gear and motor that allow the crane to rotate. On top of the slewing unit are three parts: the long horizontal jib or working arm, the shorter horizontal machinery arm, and the operator's cab. The long horizontal jib is the portion of the crane that carries the load. A trolley runs along the jib to move the load in and out from the crane's center. The shorter horizontal machinery arm contains the crane's motor that lifts the load, control electronics that drive the motor, large concrete counter weights, and the cable drum. The operator's cab is where the operator sits and controls the crane.
Tower cranes are typically located on top or near the top of buildings so that they can reach different parts of the building with ease to lift and drop materials and are very important for any new building built beyond a certain height. Tower cranes can be fixed to the ground on a concrete slab, or suspended off the ground and mounted to a structure. Tower cranes can use their own hoisting power to increase their height.
Three common methods of increasing the height of a tower crane are: the external climbing method, the internal climbing method, and the sky-crane method.
The external climbing method uses the crane's working arm or jib together with the crane's mast to expand the crane upward along the outside of the building. The base of the crane is fixed in a concrete slab in the ground, and the crane's mast is erected adjacent the building using smaller mobile cranes. Once the building reaches a certain height (typically about 180 feet or 15 stories), the crane is fastened to the building with steel collars, and new mast segments are inserted into the crane's existing mast. The crane has a special climbing section, in the form of a large metal sheath that scales the outside of the crane's mast, which is used to add new mast segments to the mast. The climbing section raises the crane's working arm above the last installed and stable mast segment and temporarily supports the working arm. A space in the climbing section is provided to take in a new mast segment, raised up by the crane's arm, and to hold the new mast segment temporarily while workers bolt the new mast segment into place. Using the external climbing method, the crane first constructs a section of the building, the crane is fastened to that section of the building, and then the crane receives new mast segments to grow taller.
The internal climbing method uses the crane to build new floors from the inside of the building. After a few new floors have been finished above the crane, the crane is advanced to a higher spot inside the building. When using the internal climbing method, the crane is typically positioned inside the center of the building, in a kind of makeshift courtyard, where the crane constructs the building (e.g., skyscraper) around itself. A hydraulic cylinder at the crane's base elevates the crane through the hollow core of the building to a higher floor. The hollow core is typically composed of a durable material such as concrete. Workers then slide steel beams underneath the crane to provide a sturdy new footing, and then the crane can continue to be used for construction tasks (i.e., building the next set of floors). Disadvantages of the internal climbing approach are the need to reinforce the building structure's outer walls to support very heavy loads, such as vertical loads of approximately 150 tons, and horizontal loads of approximately 40-50 tons, and that positioning the crane in the center of the construction can interfere with the construction process.
In the sky-crane method, the crane is airlifted by a heavy-lift helicopter and flown to the top of the building or construction site. Since a single segment of a crane's mast can typically weigh between 3,000 and 20,000 pounds, the lifting of the crane is done piece by piece. Due to the high monetary cost of performing such a task, and because flying a load-bearing helicopter over a populated area is logistically very difficult, the sky-crane method is quite rare.
CN Patent Application Publication No. 103896165(A) to Lixian et al entitled “Suspension Type Outside Climbing Tower Crane Supporting System and Turnover using Method thereof” discloses support brackets installed in the building unto which embedded parts allow the fixation of crane support frames which are supported in a horizontal crane supporting or hooping position, by upper and lower diagonal rods, also fixated to the brackets by the embedded parts. A lower frame can be dismantled and used as an upper frame as the tower crane is climbed. For dismantling of the support frame from the hooped crane, the support frame is halved into two sub-frames, allowing their separation from the hooped crane and their temporary hanging by ropes.
U.S. Pat. No. 4,029,173 to Wakabayashi entitled “Foldable Scaffold Devices”, discloses an erectable and transportable gondola-like scaffold cage which includes a front frame member which is pivotally connected to a rear frame member and which may be folded into juxtaposition therewith for transportation or spaced outwardly therefrom to form a cage and which includes means for securing the entire element in position on a supporting structure such as a beam. A flexible member such as a chain, an extensible rod or a connecting plate, is connected between the upper ends of each side of the front structure to the upper ends of each side of the rear structure, and is pulled toward the rear to collapse the cage and the scaffold can be freely carried to another position as in a folded state and opened by loosening the flexible member.
U.S. Pat. No. 3,053,398 to Liebherr et al., entitled “Rotary Tower Crane”, discloses a rotary tower crane where the tower is raised by adding tower sections.
U.S. Pat. No. 3,366,251 to Strand, entitled “Climbing Crane”, discloses a climbing crane mounted to a rail, where the crane uses a hydraulic lift for elevating.
U.S. Pat. No. 3,485,384 to Nikai et al., entitled “Method of climbing a tower crane for constructing high buildings”, discloses a tower crane having a bell portion that is slidable along the crane's mast.
U.S. Pat. No. 5,645,395 to Huang, entitled “Building crane apparatus climbable on building walls”, discloses a gantry crane that climbs on rails secured to the building.
U.S. Pat. No. 7,290,672 to Davis et al., entitled “Tower Crane Device”, discloses a tower crane device with a climbing frame.
US Patent Application Publication No. 2003/0213765 to St-Germain, entitled “Tower Crane with Raising Platform”, discloses a self-erecting tower crane with tower sections and a self-raising sleeve.